GGD283_1

Rock glaciers, Disko Island, Greenland, Version 1

Version 1eng; usa

AbstractDisko Island (8600 km2) is situated west of central mainland Greenland. The island is part of the Tertiary volcanic province of West Greenland and is mainly made up by lavas. The landscape is a plateau basalt landscape with cirque carved lava plateaus and U-shaped valleys and fjords. Rock glaciers are frequent in Disko Island (Humlum, 1982). In southern Disko Island, about 60 km SSE of the two study sites, meteorological observations have been carried out since 1923 in the village of Godhavn. The present (1961-1990) mean annual air temperature is -3.9 C, the coldest month is March (-15.1 C), and July is the warmest month (7.1 C). The mean annual precipitation at Godhavn is about 400 mm water equivalent. Most of the precipitation (75 %) usually falls during the period June to December, associated with advection of moist, maritime air masses from the south and southwest along the Davis Strait. The remaining part of the year is comparatively dry, as it is dominated by cold and dry katabatic air masses flowing off the Greenland Ice Sheet to the east. Approximately 60-70 % of the mean annual precipitation is snow and in Godhavn a persistent snow cover is registered from late September to late May.
No systematic mapping of permafrost or permafrost related terrain features have been carried out in this part of West Greenland. Weidick (1968), however, places Disko Island within the zone of continuous permafrost. This is supported by the occurrence of open system pingos (Christiansen, 1995) and numerous rock glaciers (Humlum, 1982, 1984, 1988a, 1988b, 1996; Humlum et al., 1995; Rasch et al. 1996), which are geomorphic indications of the presence of widespread permafrost in Disko Island. Adopting a standard continental geothermal gradient of about 0.033 C m-1, the mean annual air temperature of -7.5 C (1991-96) indicates a potential permafrost thickness of about 175-225 m. This estimate is presumably somewhat conservative, as the Little Ice Age annual air temperature presumably was about 2C below modern values (Humlum, 1996), which would provide conditions for a somewhat thicker permafrost layer than is suggested by modern meteorological values. The high frequency of rock glaciers on Disko Island is presumably derived from high rock weathering rates (Humlum, 1992). These data are presented on the CAPS Version 1.0 CD-ROM, June
1998.